The applicants hereby expressly incorporate by reference in their entirety the description of an xe2x80x9cApparatus and Method for Imaging Small Cavitiesxe2x80x9d described in Proudian et al. U.S. Pat. No. 4,917,097, the description of a xe2x80x9cDilating and Imaging Apparatusxe2x80x9d described in Eberle et al. U.S. Pat. No. 5,167,233, the description of an xe2x80x9cUltrasound Catheterxe2x80x9d described in Eberle et al. U.S. Pat. No. 5,368,037, the description of an xe2x80x9cApparatus And Method For Detecting Blood Flow In Intravascular Ultrasonic Imagingxe2x80x9d in O""Donnell et al. U.S. Pat. No. 5,453,575, and the description of a xe2x80x9cHigh Resolution Intravascular Ultrasound Transducer Having a Flexible Substratexe2x80x9d in Eberle et al. U.S. Ser. No. 08/712,576 filed on Sep. 13, 1996 which is a continuation of U.S. Ser. No. 08/578,226 filed on Dec. 26, 1995.
This invention relates to ultrasound imaging apparatuses placed within a cavity to provide images thereof of the type described in Proudian et al. U.S. Pat. No. 4,917,097 and more specifically, to ultrasound imaging apparatuses and methods for fabricating such devices on a scale such that the transducer assembly portion of the imaging apparatus may be placed within a vasculature in order to produce images of the vasculature.
In the United States and many other countries, heart disease is a leading cause of death and, disability. One particular kind of heart disease is atherosclerosis, which involves the degeneration of the walls and lumen of the arteries throughout the body. Scientific studies have demonstrated the thickening of an arterial wall and eventual encroachment of the tissue into the lumen as fatty material builds upon the vessel walls. The fatty material is known as xe2x80x9cplaque.xe2x80x9d As the plaque builds up and the lumen narrows, blood flow is restricted. If the artery narrows too much, or if a blood clot forms at an injured plaque site (lesion), flow is severely reduced, or cut off and consequently the muscle that it supports may be injured or die due to a lack of oxygen. Atherosclerosis can occur throughout the human body, but it is most life threatening when it involves the coronary arteries which supply oxygen to the heart. If blood flow to the heart is significantly reduced or cut off, a myocardial infarction or xe2x80x9cheart attackxe2x80x9d often occurs. If not treated in sufficient time, a heart attack often leads to death.
The medical profession relies upon a wide variety of tools to treat coronary disease, ranging from drugs to open heart xe2x80x9cbypassxe2x80x9d surgery. Often, a lesion can be diagnosed and treated with minimal intervention through the use of catheter-based tools that are threaded into the coronary arteries via the femoral artery in the groin. For example, one treatment for lesions is a procedure known as percutaneous transluminal coronary angioplasty (PTCA) whereby a catheter with an expandable balloon at its tip is threaded into the lesion and inflated. The underlying lesion is re-shaped, and hopefully, the lumen diameter is increased to improve blood flow.
In recent years, a new technique has been developed for obtaining information about coronary vessels and to view the effects of therapy on the form and structure of a site within a vessel rather then merely determining that blood is flowing through a vessel. The new technique, known as Intracoronary/Intravascular Ultrasound (ICUS/IVUS), employs very small transducers arranged on the end of a catheter which provide electronic transduced echo signals to an external imaging system in order to produce a two or three-dimensional image of the lumen, the arterial tissue, and tissue surrounding the artery. These images are generated in substantially real time and provide images of superior quality to the known x-ray imaging methods and apparatuses. Imaging techniques have been developed to obtain detailed images of vessels and the blood flowing through them. An example of such a method is the flow imaging method and apparatus described in O""Donnell et al. U.S. Pat. No. 5,453,575, the teachings of which are expressly incorporated in their entirety herein by reference. Other imaging methods and intravascular ultrasound imaging applications would also benefit from enhanced image resolution.
Transducer backing materials having relatively low acoustic impedance improve signal quality in transducer assemblies comprising PZT or PZT composites. The advantages of such backing materials are explained in Eberle et al. U.S. Pat. No. 5,368,037 the teachings of which are expressly incorporated in their entirety herein by reference. It is also important to select a matching layer for maximizing the acoustic performance of the PZT transducers by minimizing echoes arising from the ultrasound assembly/blood-tissue interface.
When designing a very small device for manufacture in large quantities it is important to take into consideration practical limitations such as manufacturability, reliability, resiliency and performance. The ultrasound catheter assembly must produce high quality raw image signals for the signal processing system located outside the body within which the intravascular ultrasound transducer assembly is inserted for imaging. However, there is an interest in limiting the number of parts since added complexity can increase the manufacturing costs and reduce the yield of the intravascular ultrasound catheter assemblies. The devices must be sufficiently resilient to withstand handling during manufacture and use.
It is a general object of the present invention to improve the manufacturability of an intravascular ultrasound transducer assembly.
It is another object of the present invention to decrease the per-unit cost for manufacturing ultrasound transducer assemblies.
If is yet another object of the present invention to increase the yield of manufactured ultrasound transducer assemblies.
It is a related object to provide enhanced structural integrity of the electrical connections in the transducer assembly.
It is another object of the present invention to decrease the complexity of the ultrasound transducer assembly.
The above mentioned and other objects are met in a new ultrasound transducer assembly, and method for fabricating the ultrasound transducer assembly including a PZT substrate with metallic contacts formed directly on the PZT substrate during a pre-fabrication step.
The ultrasound transducer assembly of the present invention includes a flexible substrate having an inner surface to which transducer signal lines and a ground line are attached to form a flexible circuit. In a preferred embodiment of the present invention, the flexible substrate provides the quarter-wave matching layer for the ultrasound transducers.
An ultrasound transducer array and integrated circuitry are attached during fabrication of the ultrasound transducer assembly while the flexible substrate is substantially planar (i.e., flat). In accordance with an aspect of the present invention, the signal electrode and ground electrode for transducer elements at least partially extend to the surface of the transducer elements that establishes contact with the inner surface plane of the flexible circuit. As a consequence both the ground and signal electrodes can establish direct electrical contact with corresponding signal and ground pads on the flexible surface. Therefore, conductive bridges between flexible circuit lines and electrodes located on a physically remote surface of the transducer elements are no longer required.
In a particular embodiment of the invention, after the transducer array and integrated circuit chips are attached to the flexible substrate, the flexible substrate is reshaped into a substantially non-planar shape around a lumen tube to form a substantially cylindrical shape. In accordance with another, more particular, aspect of the present invention, the spaces within the ultrasound transducer assembly between the lumen tube, the flex circuit, the transducer array and the integrated circuits are all filled with a backing material characterized by relatively low acoustic impedance. While the use of backing material in the area of the integrated circuits may reduce the physical rigidity of the ultrasound transducer assembly, in accordance with yet another aspect of the present invention, metal discs are placed upon the lumen tube of the assembly and enhance the physical integrity of the device. The metal discs also form part of a path from a ground wire to the ground electrodes of the ultrasound transducer array elements.
The integrated circuitry is housed within integrated circuit chips on the ultrasound transducer assembly. The integrated circuitry is coupled via a cable to an imaging computer which controls the transmission of ultrasound emission signals transmitted by the integrated circuitry to the ultrasound transducer array elements. The imaging computer also constructs images from electrical signals transmitted from the integrated circuitry corresponding to ultrasound echoes received by the transducer array elements.
The above described new ultrasound transducer assembly and method for making such a device retains a two-dimensional aspect to the early stages of ultrasound transducer assembly fabrication which will ultimately yield a three-dimensional, cylindrical device. Furthermore, the flexible circuit and method for fabricating an ultrasound transducer assembly according to the present invention facilitate the construction of individual, physically separate transducer elements in a transducer array. Finally, the present device eliminates a number of structures which contributed to the complexity of the ultrasound transducer assembly and the method for making such a device.